The use of USB electronic keys is commonplace, used by electronic devices such as personal computers, mobile telephones, printers, etc. all of which are peripheral ports of these devices. These keys can comprise various functions, including memory, security or other functions.
They must adhere to a standard which defines notably the mechanical and electrical characteristics of the USB interface. A USB key complying with the standard must thus comprise a male connector while the USB peripheral ports of electronic devices must comprise female connectors. Additionally, a USB key comprises a part which is not introduced into the connector and which notably allows it to be gripped. The whole assembly must offer mechanical resistance to torsion and to bending.
The male connector is defined by its dimensions and notably its thickness, the position and the width of the contact pads, and their allocation, which must correspond to the counter-contacts provided in the female connector. An end-on view of a female connector F, with a sectional view of a USB male connector M, is illustrated in FIG. 1. It shows the arrangement 1, 2, 3 and 4 of the counter-contacts cc corresponding respectively to the power supply VDD, to the data link wire D−, to the data link wire D+ and to ground.
When the connector M of the key is introduced, its contact pads pc each come respectively into contact under a corresponding counter-contact cc, held by locking means 5 and 6 provided in the female connector.
In order for connection to take place correctly, the thickness of the male connector must substantially correspond to the standardized space left free between the counter-contacts and the locking means. This standardized thickness dK is of the order of 2 millimetres.
USB female connectors exhibit the feature of mechanically allowing the insertion of the connector of a key in a correct manner as indicated in FIG. 1, but also in the opposite orientation, that is to say in the example of the figure, contact pads downwards in the figure, which does not allow electrical connection. This feature causes an impediment to the use of these keys. It is thus useful to furnish these electronic keys with a mechanical polarizer.
According to the state of the art, mechanical polarizers such as these are provided in electronic keys which are made from a printed circuit, with the contact pads of the connector at one end, the remainder of the circuit being encapsulated in a protective plastic cover. In these keys, a shielding ring is generally provided, around the connector, which forms a mechanical polarizer: the ring abuts against the frame of the female connector if the connector is introduced wrongly. However, these keys are expensive to manufacture. Furthermore they leave few possibilities of graphical customization, which is possible only on the cover, and this customization is also expensive.
Other manufacturing techniques have been researched in order to reduce the cost of these keys. Notably, the French patent application published under the number FR 2 830 107 discloses a method of USB key manufacture which uses manufacturing steps borrowed from the well-known techniques for manufacturing chip cards, whose reference standard is the ISO/IEC 7816 standard. These manufacturing techniques comprise the steps of manufacturing the card body, by plastic moulding, or else by laminating thin plastic sheets from commercially available sheets, precutting steps, notably to make the detachable mini-cards in the SIM format, steps of mounting the modules or microcircuits with the contact pads, by machining a cavity and fixing and transferring the module or microcircuit into the cavity so that the pads of the contact of the module are flush with the surface of the card. These various steps are well known to the person skilled in the art.
These manufacturing techniques have been designed to make it possible to produce low-cost chip cards. Furthermore, if at least some steps for manufacturing the key correspond to the techniques for manufacturing these cards, it is possible to manufacture these keys on already existing chip card manufacturing lines—hence an additional reduction in costs. But these keys pose a connectivity problem, on account of the difference in thickness between the chip cards and the USB keys, at least of their USB connector. Specifically it has been seen that the standardized thickness of a USB key (male) connector is of the order of 2 millimetres. A chip card in the ISO format has a standardized thickness of 0.76 millimetres, that is to say less than half as thick. This thickness does not make it possible to achieve correct and reliable contact with the counter-contacts of a USB female connector. To solve this problem, the aforesaid French patent application envisages the use of shims or an adaptor, thereby complicating the manufacture and/or use of the key and increasing its cost. Additionally no mechanical polarizer is envisaged.